Diamond is the hardest substance in known natural world which is 1000 times the absolute hardness of quartz. Accordingly, diamond is widely applied to the field of grinding process of various hard materials due to its incomparable high hardness and excellent mechanical physical performance. Diamond micro powder, regarded as the hardest ultrafine abrasive, is the ideal material for grinding and polishing hard materials, such as cemented carbide, ceramica, gemstone, optical glass, manual crystal. Wherein, a monocrystalline diamond micro powder is obtained through the pulverization and classification of diamond synthesized by a static high-pressure method which has a microscopic morphology of irregular polyhedron with an acute edge angle, so as to provide a strong grinding force. However, the sharp edge angle is very easy to scratch the surface of a workpiece when using the monocrystalline diamond to grind and polish the workpiece, thereby more working procedures for repairing the aforesaid scratches are needed in order to reach the requirement on a higher flatness of the workpiece surface.
As the development of ultra-precision grinding and polishing technology, the researchers find when heat treating a diamond micro powder with some metal coating, the metal coating can promote a phase transformation from diamond to graphite; then the metal coating on the diamond surface is cleaned and dissolved by using common acid and non-diamond carbon on the surface of diamond micro powder is removed by using oxidative acid, the treated monocrystalline diamond micro powder presents a unique rough-surface morphology and further presents a plurality of contact points and contact surfaces during grinding and polishing process, therefore it has good self-sharpening.
The Chinese patent document of CN102245730A discloses a monocrystalline diamond particle having a unique morphology, and a metal is coated on the monocrystalline diamond particle surface by the following two methods, method 1: adopting the electroless nickel plating to form a nickel coated diamond, the specific operating steps are as follows: (1) subjecting the uncoated diamond particles to contact a solution of colloidal palladium so as to make the fine palladium particles uniformly absorb onto the surface of the diamond, the activating treatment on the surface of the diamond micro-powder by using the palladium particles enhances the auto-catalyzed property of the electroless deposited nickel on the surface of the diamond micro-powder; (2) placing the activated diamond into nickel sulfamate solution containing 10 g/L dissolved nickel and simultaneously adding a sodium hypophosphate and maintaining the temperature at about 80° C., when the dissolved nickel in solution will autocatalytically deposit onto the activated diamond surfaces method 2: adopting a mix-compress manner of diamond micro powder and iron powder to form an intimate mixture of diamond particles and iron particles, the specific operating steps are as follows: (1) mixing diamond particles and iron powder in the mass ratio of 1:9-1:4, adding a certain binder to provide lubricity to particle surface so as to allow a denser packing and intimate contact between the iron powder and diamond, thus the mixture is compressed to form a intimate mixture of diamond and iron powder in the form of a pellet, an aggregate or other compressed mixture; (2) then heat treating the prepared metal-coated diamond particles by the above two methods in a vacuum atmosphere, hydrogen atmosphere or inert gas atmosphere in the temperature range of 650-1000° C. for 0.5-5 hours, so as to achieve an graphitization of the diamond surface, and then cooling the heat treated particles; (3) finally, processing acid cleaning and non-diamond carbon dissolution to obtain the monocrystalline diamond particles having a unique morphology. However, in the method 1, a high activation treatment degree of diamond particle surface is required in the electroless nickel plating process, otherwise an integral and uniform nickel coating layer is difficult to form, additionally, a large number of discard solution containing nickel will be produced after electroless plating, thus increasing the cost for treating the discard solution. While adopting the method 2 may effectively avoid the above problems. However, in method 2, the adopted iron powder and diamond micro powder are both at micron scale, and the micron-scale monocrystalline diamond particle and micron-scale iron powder have a insufficient contact when mixing them, resulting in a difficulty to form a integral and uniform iron coating layer on the monocrystalline diamond particle surface, further the microscopic morphology of the product shows that a larger pit emerges on the surface of the monocrystalline diamond particle produced by this method. Additionally, when mixing the micron-scale iron powder and micron-scale diamond micro powder, the amount of iron powder is a plurality of times of diamond micro powder so as to ensure a sufficient surface contact of the iron powder and diamond particle, both causing waste of raw material and increasing burden and cost of acid post-treatment.